1. Field of the Invention
The present invention is related generally to electronic current sensor type circuits and more particularly to such type circuits for use in electronic metering devices wherein phase inversion or amplitude-mark-space modulation (time division) techniques are employed to make precision measurements of alternating current and/or voltage.
2. Description of the Prior Art
While the present invention has application in most any environment where the magnitude of a large AC signal has to be sensed and/or measured, it finds particular application in such devices as watthour meters, watt-transducers and the like.
In recent years, electronic watt-hour or energy consumption meters have come into existence, with the expectation that they will one day replace the older prior art induction type meters. This electronic metering technology is still in the refinement stages of development. Three such type electronic energy consumption meters are disclosed in my U.S. Pat. Nos. 3,955,138; 3,875,509, and 3,875,508. The entire disclosure of these earlier patents is hereby incorporated by reference. The entire right, title and interest in and to the inventions described in the aforementioned patents and the entire right, title and interest in and to the invention herein disclosed, as well as in and to the patent application of which this application is a part, are assigned to the same assignee.
One major problem in electronic watt-meter design is to sense or measure the magnitude of the current of an AC signal with high precision, while simultaneously inverting that signal in a circuit which utilizes a minimum amount of power and which presents the lowest possible load or impedance to the circuit being monitored. While the above mentioned precision is possible with the use of large and expensive electrical and electronic components, the cost and size of those components quickly removes the economic incentive for a user to purchase a meter using such components. As such, a need exists for a universally usable AC sensor circuit design having phase inversion or mark-space-modulation capabilities which can be fabricated from small low cost components and which design provides for virtually powerless sensing of the magnitude of the current of an AC signal.